If I understand you correctly, here is your problem:

"I try to get it running with very little elevator just to keep the tail down on initial roll out"

You want to hold enough up elevator initially to keep the model from tipping over on its nose when you initially apply throttle, but that is all. The goal is to get the tailwheel off of the ground as soon as possible and to steer with the rudder. This way, your Cub won't take off prematurely and stall.

Don't forget to hold a bit of opposite aileron if you are taking off crosswind. Opposite to the direction the model is trying to roll from being blown, that is. Roll the model slightly into the wind.

Good luck.